Enciphering and deciphering system



C. l. CRONBURG ENCIPHERING AND DECIPHERING SYSTEM lNvE/'NTOR C, I. Cra/@bourg BY ATTORNEY YFiled Feb. 12, 1944 Patented July 9, 1946 UNITED` STATES PATENT ,OFFICE 2,403,888' t Y i ENCIPHERTNG AND DECIPHERING SYSTEM Claude Irving Cronburg, ClevelandrHeights, Ohio, assigner to American Telephone and Telegraph Company, a corporation of New York Application February 12, 1944, Serial No. 522,039Y

14 Claims. l

This invention relates to teletypewriter .communication systems and more particularly to arrangements for enciphering and deciphering messages sent over such systems.

In the art of communication by means of lteletypewriters, messages are sent by means of the Baudot code. This code usually comprises five characters determining pulses each of which may be either a marking or a spacing pulse depending upon the character. Where start-stop distributors are used to transmit the pulses to the line or receive them therefrom in successive order, two additional pulses, one for starting and one for stopping the distributor, are usually added to the ve pulses of the Baudot code.

Heretofore various methods of attaining secrecy in the transmission of messages by such codes have been proposed. Such methods usually involve some arbitrary variation or change in the ve Baudot pulses without affecting the start or stop pulses. These variations usually take the form of changes in the character of the individual pulses. Usually enciphering is accomplished by scrambling the code combinations representing message characters with arbitrary character c ode .combinations punched in a tape in a random manner. To decipher the message at a receiver the enciphered message is scrambled with a similar cipher tape, so that the resultant codes are restored to the form of the original message codes.

Enciphering and deciphering by means of cipher tapes have certain objections due to the impermanent character of the tape, the ease with which it may be prepared by unauthorized persons breaking the cipher, etc. There is .consequently a need in the art for an enciphering and deciphering arrangement employing durable mechanical elements so designed that any desired cipher code may be set up thereon at will.

To accomplish this result the present invention utilizes mechanical switches, preferably of the step-by-step type. The switches have ve banks of code-determining contacts over which wipers may be advanced. By variably wiring corresponding contacts in each of the ve banks for each position of the switch a diierent Baudot code combination may be set up in each switch position so that the cipher code combination will be changed each time the switch is advanceda step. By employing a sufficient number oi suchl switches and suitably varying the wiring of thel contact points of the different switches, the vef unit cipher code for any individual character will depend upon the code Wiring of a plurality Yof switches, and ywil1 vary in accordance with the relative settings of the severalsswitchesmThis enables a scrambling cipher to be obtained which involves an enormous number of random code combinations to be used'befo're the pattern is repeated. f Y g Y Y Y In-accordance with the' invention the switchesare preferably wired so as to introduce two types of Variation into each individual code'combina-U tion. Certain of the switches may be wired `to scramble the code combination` by superposing an arbitrary cipher code thereon, and'others may be wired to produce-changes analogous to pulse reversals in thecharacter of some or all of the individualpulseslhFor example, by the first ofthese effects the pulses of acharacten instead of being' transmitted normally-Amay be trans mt'ted in the form of a code combination for` an entirely dierent character. By the second efiect, if the ve pulses are inltherform mark-spacespace-mark-space, for example, their character may be changed to spacelmark-space-spacemark, this', result being attained by inverting the iirst, second, fourth and fth pulses.

AnoA her featureof the invention resides in the` use of a vacuum tube distributor instead of the usual mechanical distributor. In the mechanical type of distributor a brush rotates over'successive ring segments corresponding Vtothe start puls, five character determining pulses and the stop pulse. In V`accordance with the present invention ya corresponding function is obtained by a combination of vacuum tubes and associated circuits. The vacuum tubes used` in the improved distrbutor may be lof any known type, but prefeiallolyY gas tubes Voi the so-called trigger type are employed. These tubes, in association with certain timing circuits involving condensers and resistances, and certain counting relays, function to distribute a series of pulses to a plurality ofv successive circuits,

While separate tubes may be used for each pulse transmitted, so that Vther number of, tubes willbeV identical with, or a multiple of, the number of pulses, it is preferred to utilize the same tube for timing all of the pulses. This is possible because fin practice all of the pulses" except the stop pulse are of the same length. The tube with its timing circuit is used to successively-,operate counting relays f orthe start pulse and ve character-determining pulses. For the longer stop pulse the constants ofy theV timing circuit n associated withY the tube are changedtoproduce a longer pulse interval. y Y Y K, e

The distributor ordinarily used with enciphering arrangements is of the receiving type. In this type of distributor the pulses are regenerated by transmitting a renewed pulse during a limited part of the pulse interval and preferably near the middle thereof. Therefore, the invention contemplates a second tube associated with a timing circuit for determining the period of duration of the renewed pulse, and for adjusting or orienting such period with respect to the total interval assigned to the pulse. This tube, like the tube which times the pulse intervals, repeats its operating cycle for each pulse transmitted.

While as herein illustrated the improved vacuum tube distributor is used only in connection with the enciphering circuit, it will be understood that it may be used in connection with any piece of apparatus and in any type of circuit requiring a distributor.

The invention will now be more fully understood from the following description, when read in connection with the drawing, the single figure of which illustrates a preferred circuit arrangement embodying the invention.

GENERAL DESCRIPTION F APPARATUS The circuit arrangement and apparatus of the invention include three main pieces of equipment: (a) a repeater RPR for repeating signals from the line L to a receiving teletypewriter TTY in a loop SL, and for repeating signals from the loop SL to the line; (b) a vacuum tube distributor VTD; and (c) a mixing circuit MCT for determining the cipher with which the message is to be scrambled. In the diagram the repeater is shown in the lower left-hand portion of the drawing, the vacuum tube distributor in the upper part of the drawing, and the mixing circuit in the lower right-hand portion of the drawing.

(a) The repeater The repeater is of the reversible type, this being necessary in order that the mixing circuit, which is a one-way circuit, may be pointed in the correct direction depending upon whether signals are being received from the line L by the teletypewriter TTY in the loop SL, or transmitted from the transmitter MTS in the loop to the line. The essential elements of the repeater include four polar relays. (l) a relay LR for receiving signals from the line L, (2) a relay LS for transmitting signals to the line, (3) a relay TR for receiving signals from the transmitter MTS, and (4) a relay TS for sending signals to the teletypewriter TTY.

In order to prevent the relay LS from sending signals to the line L when signals are incoming from the line, and likewise to prevent the relay TS from sending signals to the teletypewriter TTY when the sender MTS is sending out signals, an additional polar relay RV is provided. This relay normally functions to lock up the relay LS so that signals may be received from the line L without interference on the part of the relay LS. When, however, signals are sent out from the transmitter MTS, the first signal shifts the armature of the relay RV to its sending position and locks it -in that position so that the relay TS is locked up and the relay LS is unlocked. Relay LS may now repeat signals to the line L and the relay TS is prevented from responding to signals sent out from the loop SL to cause interference in said loop.

The repeater is associated with the enciphering and deciphering arrangements through polar relays S and R. The relay R responds either to signals repeated from` the line L through the relay LR or to signals repeated from the loop SL through the relay TR. Signals from either source are therefore transmitted by the relay R through the distributor shown in the upper portion of the drawing to the mixing circuit shown in the lower right-hand part of the drawing. The relay S, on the other hand, responds to signals which have been passed through the mixing circuit regardless of whether they were originally received from the line L or from the loop SL. In the latter case the signals are repeated by the relay S to the relay LS, to be transmitted to the line L. In the former case they are repeated by the relay S to the relay TS toI be transmitted to the loop SL and be recorded on the teletypewriter TTY.

The loop SL, with which the repeater is associated, includes in addition to the teletypewriter TI'Y for recording either incoming or outgoing signals, a message tape sender or transmitter MTS (or, if preferred, a keyboard transmitter) with which is associated the usual transmitting distributor TD which, in this instance, is of the ordinary transmitting type in which a brush passes over successive segments to successively transmit pulses of a code combination.

(b) Vacuum tube distributor The distributor includes essentially a starting relay STT, a timing vacuum tube TVT; and associated condenser and resistances for timing its operation, an orienting vacuum tube OVTz, 'an orienting relay OR., counting relays Si to S5,inclusive, a stopping relay STP included in the counting relay chain, and a release relay REL. In addition, certain auxiliary relays R1, R2, Ra and R4 are provided. The function of these relays will Yappear more fully hereinafter.

The relay R4, the counting relays S1 to S5, inclusive, stopping relay STP, and release relay REL each have their windings connected to positive battery through a suitable resistance such as a in the case of relay R4, r1 to T5, inclusive, in the case of relays S1 to S5, inclusive, b in the case of relay STP, and c in the case of relay REL. The current flowing through these resistances is insufficient to operate these relays. However, when the relays are operated by battery connected directly to their windings, the current owing through their resistances acts as a holding current to maintain them operated and, in effect, lock them up, as will be made clear later.

When a start impulse is relayed from the repeater to the distributor through the relay R of the repeater, the relay R4 is operated to initiate the action of the distributor. Relay R4 operates and locks up the starting relay STT and also conditions the orienting vacuum tube OVTz for operation. The starting relay when operated remains locked up until the complete cycle of seven impulses has been transmitted. The orienting Vacu-um tube OVTz when conditioned for operation does not immediately trigger off, ibut its action is delayed for a predetermined time while the condenser C2 is being charged through the resistance T2. The latter may be adjusted to cause the tube to discharge or trigger off at any desired interval after the initiation of the start to the relay S associated with the repeater. 7S The 'operation of the start relay STT condieficaces tions the timing vacuum tube TVTi. for opera-V tion to time the impulses. The-tube does not operate immediately, however, because the associated condenser C1 and resistances T1 and T1 are of such value that it requires 22 miliseconds to build up a potential on the controlling electrode of the tube which will cause a discharge to take place between its cathode and anode. Upon triggering off, however, it operates the relay R1, which in turn operates the relay R2. It also releases relays Rs and R4, the former having in the meantime been operated by the vacuum tube OVT2 as already described. Relay R2 immediately short-circuits the relay R1 and the tube TVT1, the relay R1 at oncev releasing relay R2. The momentary short-circuiting of the tube TVT1 restores the tube to normal so that it is again conditioned for operation, and .repeats its cycle to again trigger oi at the end of 22 milliseconds, thus establishing the period for the first character-determining impulse.

The momentary operation of the relay R2 operated the first counting relay S1. During the interval required for the second operation of the tube TVT1, the orienting relay OVT2 operates as before, so that the orienting relay OR for a brief interval transmits the first character determining impulse relayed by the relay R of the repeater to the mixing circuit.

The circuit arrangementv of the distributor is such that the tubes TVTi and OVT2 continue to repeat their cycles during successive 22-millisecond intervals, and successive counting relays such as S2, S3, Si and S5 are operated and transmit successive character-determining impulses to the mixing circuit, as will be described more fully later. After the last character-determining impulse has been transmitted, the next relay in the chain, which is the stop relay STP, is actuated. This changes the timing of the tube TVT1 so that it now requires .31 milliseconds, the normal length of a stop pulse, before it triggers off.

During the stop impulse, the orienting relay OR is operated just as in the case of the other impulses but, due to the fact all of the chain relays have been operated, the momentary start impulse controlled by the orienting relay OR is transmitted directly to the relay S of the repeater and not through the mixing circuit. At the end of the 31-millisecond interval the release relay REL is momentarily operated and releases all of the relays of the distributor so that the distributing apparatus is ready to execute a new code cycle in response to the next start impulse.

The character-determining impulses are not transmitted directly to the relay S of the repeater but rst pass through the mixing circuit to be enciphered, and are then transmitted from the mixing circuit to the relay S as will be described. The full sequence of seven impulses is relayed by the relay S through the repeater to the line L or to the loop SL, depending upon whether they originated in the loop or in said line.

(c) Mixing circuit The mixing circuit as illustrated includes four 22-point step-by-step Switches SW1, SW2, SW3, and SW4. Each of these switches has six contacts in each of the 22 rows comprising a bank.-

of the 22 rows of the bank is used to control the ofthe switches are so wired that the switch SW1 will be `advancedone step each time a full set oci' seven code pulses is transmitted, thereby changing .the enciphering code as will be described later. When the rst switch SW1 has thus been advanced to its twenty-second point, the circuit is automatically closed to advance the second switch SW2 one step. After this switch has been `advanced 22 steps (the switch SW1 having in the meantime rotated through its complete cycle 22 times), the switch SW2 automatically completes a circuit to advance the switch SW3 one step. Switch SW3 after being advanced 22 steps, in turn advances switch SW4 one step. In `this manner a large number of diilerent ciphering combinations may be produced for scrambling successive message code combinations (or for -unscrambling received enciphered code combinations) as will be more fully described later.

The switches SW3 and SWi are so arrangedV as to superpose a cipher in the form of a code representing some arbitrary order on the live message character-determining impulses. The five message character-determining impulses are transmitted through the distributor to the ve vertical rows of contacts of the switch SWi 1ocated at the right of the vertical row of contacts numbered l, to 22, inclusive, which latter are used in connection with the stepping operations of the switches. The five character pulse contacts in each row of the switch are wired so :that in diierent positions of the brush B4 the pulses` are changed in order. For example, it will be seen that the top row of contacts of the switch SW4 are arranged in normal order I-'2- 3-4-5. are numbered in the order I-2-3-5-4, and the twentieth row of contacts in the order` 5| 2-3-4. Each 0f these represents a different arbitrary ciphering character. Because of the complication of the wiring involved, only the wiring for contact numbered I is shown. It may be treated from the iirst contact in the twentysecond row through vvarious contacts numbered I in the other rows, ending with the extreme right-hand contact of the lower row, Where the order of numbering of the contacts is 5-4-2- The five pulse transmitting wipers of the brush B1 are connected, respectively, to corresponding wipers of the brush B3 of the switch SW3. This switch is also wired to change the order of num-4 bering of the contacts in each successive row although, of course, the changes are different than they are in the case of the switch SWi. To avoid complication, only the wiring for two contacts in each row is shown. VFor example, in the twenty-second row the wiring for the fourthcontact startsat the second pulse-determining contact from the left in that row, and may be traced through successive contacts numbered 4 down to the left-hand pulse-determining contact of the first row. Similarly, the wiring for contact numbered 5 starts with the fth extreme righthand contact of the twenty-second row and may be traced through successive contacts down to the y The contacts of the twenty-first row contacts of both switches, the setting determined by a particular row of the switch SW4 may be changed with respect to at least some of the pulses by the row of contacts upon which the switch SW3 is set. Consequently, in effect two successive shifts in relation occur independently, thus multiplying the possible number of combinations. Obviously a larger number of possible combinations may be obtained by interpolating additional switches similar to SW3 and SW4 between said switches.

Switches SW1 and SW2 while similar .in structure to switches SW3 and SW4t are wired to obtain a dilerent result. The function of these two switches is to determine whether the pulses transmitted by the ve wires leading from the switch SW3 will be applied to the No. 3 terminal or the No. 6 terminal of the polar relay S in the repeater. In these switches the numbers applied to the five code-determining contacts in each row indicate whether the connection is to :be completed to the one terminal or the other of the .relay S.

In the case of switch SW1, if a particular wiper of the brush rests n a terminal numbered 3 or 5, the connection is completed directly from the corresponding wire of the switch SW3 to the conductor 3 or S as the case may be, leading to the relay S. In the case of contacts marked X, however, of which there is at least one in each row in the switch SW1, the connection is extended from the switch SVH over one of the conductors marked l, 2, 3, l and 5, leading from switch SW1 to corresponding wipers of the brush B2 of switch SW2. In this case the pulse passing over the Contact marked X will arrive at one of the terminals of the relay S over a path determined by the setting of the brush B2.

For example, if as shown in the drawing, the fth wiper of the brush B1, is resting on the X contact of the second row of switch SW1, it will be seen that this contact and other similarly marked contacts in the same vertical row are all connected over wire No. 5 leading from switch SW1 to the fifth wiper of brush B2 of switch SW 2. Since in the setting there shown this fth wiper rests 0n a segment numbered 6, which is connected to conductor 6 leading to the relay S, the circuit will be completed to terminal numbered 5 of said relay.

In eect the switches SW1 and SW2 serve to introduce a different kind of translation or cipher into the code combination. The eiect of these switches is to reverse or not reverse any given pulse of the five character-determining pulses, depending upon the setting of the two switches. Another way of looking at it is that the switches SW1 and SW2 have the effect of introducing changes in the polarity of certain of the pulses, in addition to the ciphering eiect introduced through the agency of the switches SW3 and SW4.

In considering these switches it should be noted that the five pulses transmitted successively through the distributor enter the upper row of the switch SW4 rst. They are then passed by the brush B4 of said switch to the brush B1. of the switch SW3 and out over the conductors l, 2, 3, 4 and 5 leading from said switch to the brush B1 of the switch SW1. From this point the pulses are transmitted either directly through contacts of the switch SW1 to the conductors 3 or 5 leading to the relay S; or, where X contacts are involved, they are led to one or the other of the wipers numbered I to 5,

8 inclusive, of .the brush B2, 'and thence over `corresponding contacts to Aone or the other of :the conductors 3 `or leading to the relay S.

DESCRIPTION OF OPERATION (d) Operation of the repeater when sending from the Zoop SL to the line L-start impulse Let us assume that :a message in non-'ciphered form is punched in the tape and the tape is fed into the message tape sender MTS. When the operator desires to Vsend this message the key CK is closed to energize the start magnet, STM of the rotating distributor TD. This distributor when released rotates continuously at, a constant speed and as its wipers pass `from the stop vsegment to the start segment a :start impulse (which is a spacing or open circuit impulse) is sent inlto the loop SL. As the wipers pass successively over the segments marked l, 2, Y3, 4 and 5', the five character-determining pulses are vtransmitted to the loop. These pulses may be open o'r closed circuit pulses, depending upon whether the armatures of Vthe transmitter rest upon marking or spacing contacts.

If it rests upon a marking contacta `circuit is completed trom positive battery, through the distributor and loop SL, thence through the teletypewriter TTY, through the upper winding of the relay over the marking contact of the relay 'TS to negative battery. Current ows through the lower vwinding-of the relay TR 'in such direction as to bias the armature of the said relay towards its spacing contact. The current; flowing over the path just traced through the upper winding, however, is sufficient to move the armature of the relay TR to .its marking Contact notwithstanding the biasing eiect of the lower winding. If, however, 'any particular pulse entering the loop from the sender MTS is an open circuit pulse, Vas will be the case when the vcorresponding contact of the .sender is on its spacing Contact, no current will ilow through the upper winding of the relay TR. Consequently the current through the biasing Winding will shift the armature to its spacing contact. The armature of the relay TR, therefore, follows the marking and spacing character of the pulses 'transmitted into the loop SL.

As the brush of the distributor TD leaves th'e last segment and .passes over its stop segment, a closed circuit impulse is transmitted to the loop SL. This energizes the upper winding of the relay TR in the repeater and causes the armature of said relay to move to its marking contact. The code combination thus transmitted to the loop is recorded in non-ciphered form on the teletypewriter TTY. It is changed into enciphered form, however, after it leaves the loop and 'before being sent to the line L. In the meantime the brush continues through its succeeding cycle to transmit the pulses 0f the next code combination.

Returning to the rst code combination transmitted, it will be recalled that the first pulse was a spacing or no-currentI pulse which caused the relay TR to move its armature from marking to spacing. This completes a circuit from positive battery, through the middle winding of the polar relay RV, over the spacing contact of the relay TR, and through the upper winding of the relay R to negative battery. The current flowing through the middle winding of the relay RV shifts the armature of the relay from its upper or receiving contact toits .lower vor sending contact The armature is locked in this position by a circuit completed from negative battery, through the V100-ohm resistance, over the sending contact of relay RV, through the upper winding of said relay, to positive battery through the 11,000- ohm resistance. The current through this circuit is small, but suicient to hold the armature of relay RV upon its lower contact. The relay RV thus remains locked up until a stronger pulse of opposite polarity from the line L operates through the lower winding of said relay to shift its armature to its reeciving contact. Relay RV when thus locked up completes a circuit through the lower winding of the relay TS. The circuit throgh this winding holds the armature of relay TS upon its marking contact regardless of Whether marking or spacing .pulses flow through its upper winding TS.

Returning now to the circuit traced through the middle winding of the relay RV and the upper winding of the relay R, it will be noted that the current flow is in such a direction through the upper Winding of relay R as to shift its armature to its spacing contact. A circuit is thus completed from positive battery 4through the 3500- ohm resistance, over the spacing contact of the relay R, and over a circuit including conductor ST, as will be described later, to initiate the operation of the distributor. At a suitable point during the 22-milliseconds time allowed for the start impulse of the distributor, the distributor in turn sends a spacing impulse over a circuit that will be described later, yto the conductor 3 leading to the No. 3 terminal of the relay S, the circuit continuing through the upper winding of said relay over its No. 6 terminal, through a 775- ohm resistance, and thence through the lower winding of the relay R to negative battery. The current iiow over this circuit is in such a direction as to aid in holding the armature f the relay R upon its spacing contact.

The current ilow through the upper winding f of the relay S is in such a direction as to shift its armature from its marking to its spacing contact, thus completing a circuit from positive battery, through a G-ohm resistance, over the spacing contact and armature of relay S, through a 10,000-ohm winding and through the lower winding of relay S to negative battery. This current is in such a direction as to hold the armature of relay S on its spacing contact, but is not of suicient strength to prevent the armature from being shifted to its marking contact in response -to a marking current through the upper winding of said relay S.

The operation of the relay S to its spacing contact also connects positive battery over the spacing contact and armature of relay S, and thence in parallel through the upper windings of relays LS and TS to negative battery. The relay TS is not affected by the current flowing through its upper winding, however, as its armature is locked to its marking contact by the current iiowing over the sending contact of relay RV and through the lower Winding of relay TS. In the case of the relay LS, however, its lower winding is open-circuited and its armature responds to the current flowing through its upper winding, thus shifting to its spacing contact. This opens the line L and sends a start impulse to said line.

In the operations above described the relay LS has opened the line L to send a spacing impulse and, as will be described later, it responds to determining impulses, and nally, the stop im 10 pulse. `In this connection itV should be noted that the receiving Vrelay LR is used for transmitting signals from the line L to the loop SL. Since this.

relay is in the line L it will follow the operations..

This cannot-be perof the relay LS if left free. mitted because its reaction in the line L would break up the outgoing signals. Y

A contact CC is therefore provided in connection with the sender which, when closed, will opcrate the relay CT. This contact is Varranged to close just before the start signal is transmitted by the sender and to open after the th characterfdetermining impulse is transmitted. 'Ihe re-` lay CT is thus operated each time the contact closes, and applies positive battery through la Z50-ohm resistance .to a point between the .bi as.r ing winding of the relay, LR and the 1,000l-ohm resistance in circuit therewith. The bias eiect produced by the biasing winding is normally in the spacing direction. When positive battery'is applied as above described, the current in the biasing winding reverses and holds the relay LR on'its marking contact. 'I'he relay LR is thus unaiected by the signals sent to the line by the .reiayLs. f

One otherv point needs to .be considered. .The start impulse and the various character-determining impulses leaving the sender are delayed in passing through the mixing circuit by approximately rone-half a pulse length. Therefore it is necessary to hold the yrelay CT operated approximately one-half pulse length after lthe vlast character-determining impulse has been sent tothe mixing circuit. This is accomplished by making the relay CT slow torelease.. j

(e) Operation of'the repeaterwhen sending to the Zine L-character determining pulses and stopzmpulse yWe have now seenhowfthe repeateroperates to transmit a start impulse from the loop to the line L. Following this impulse the-sender MTS sends ve `character-determining pulsesl which may be either markingzor` spacing, depending upon the character tobe transmitted. Let us assume the rst of the ve character-determining impulses is a marking pulse. Positive battery will be connected over therst segment vof the distributor TD into the loop SL and will flow through the uppervwinding of the relay TR and over the marking contact 0f the relay TS to negative battery. .The current flowing through the upper winding of relay TR will be sucient to overcome the biasing action of the lower winding and will shift the armature of the relay TR back toits marking Contact.

Current will now flow from negative battery, through a '720-ohm resistance, over the marking contact of the relay LR, over the marking contact of relay TR, through the upper winding of the relay R to positive battery. The current -owing through .the upper winding of the relay R will overcome the eiTect of the current in the lower or holding windingof said relay, and will shift its armature -to its marking contact. Negative battery is now connected through a 3,500- ohm resistance and over the marking vcontact of relay R to the conductor ST. From conductor ST the circuit continues through the vacuum tube distributor VTD and the mixing circuit MCT by a path which will be described later in connection with the operation of these pieces of apparatus. Thence it continues over eitherlconductor 3 or conductor 6 leading frornthemixing circuit to one of the terminals of the upper winding of the relay S, through said operating winding, and thence through the 'W5-ohm resistance and the lower winding of the relay R to positive battery.

The current through the circuit above described is initiated by the action of the relay R as a marking current. Due, however, to the arrangements of mixing circuit MCT, as appears more fully later, the current may flow through the operating winding of the relay S in either of two directions, to produce either a marking or spacing action of the relay S, depending upon the settingA of the switches of the mixing circuit. However, it should be noted that regardless of the direction of current flow through the operating winding of the relay S the connection of the lower or holding winding of the relay R is to either positive r negative battery through 600- ohm resistances. Therefore, when the current applied to one end of the circuit is marking so that negative battery is applied to that end of the circuit, the current flow through the holding winding of the relay R will be to positive battery. Therefore, itwill be in such a direction as to tend to hold the armature of the relay R upon itsl marking con-tact. This will be true regardless of whether the armature of relay S is actuated to a marking or a spacing contact.

Similarly, if the rst pulse had been a spacing pulse, the armature of the relay R would have completed a circuit from positive battery, over the spacing contact of the relayA R, and thence over the circuit through the distributor VTD and the mixing circuit MCT through the operating winding of the relay S, and thence thro-ugh the lower winding of the relay R to negative battery. Again the operation. of. the relay S will depend upon the setting of the switches and the character of the received pulse. But regardless of the setting of the switches, the current flow through the' holding winding of the relay R would be in a direction to hold the armature of the relay R upon its spacing contact. As a result of this action the armature of the relay R is held uponA the contact to which it has been moved, even though the current through its operating windinghas ceased. There it remains until such time as the current through the operating winding is in the opposite direction, so that. it overcomes the eiect of the lower holding winding and shifts the armature.

Returning now to the relay S. This relay moves its armature to its marking or spacing contact depending upon the setting of the switches in the mixing circuit MCT and the character of the pulse received', and thereby connects negative or positive battery over its armature to the upper windings of relays LS and TS. The relay TS does not respond to this action because, as already described, its armature is locked against its marking contact by the action of the relay RV. This relay, it will be recalled, remains locked up so long as signals are sent from the local loop SL to the line L, and is only unlocked when signaling in the reverse direction commences, as will be described later. The relay LS, however, responds to the action of the armature of relay S to send into the line L a marking or spacing pulse, depending upon the setting of the mixing circuit MCT. The relay CT, of course, operates as already described to lock up the relay LR to prevent it from responding to pulses sent into the line L.

In a similar manner the other four characterdetermining pulses are sent from the distributor TD to the loop SL and operate the relay TR and the relay R, as already described, to send pulses of marking or spacing current to the conductor ST. Thence they pass through the distributor VTD and the mixing circuit MCT, through the upper winding of the relay S, and through the holding winding of the relay R to battery. The relay S therefore sends to the line L marking or spacing impulses, depending upon the received impulses and the setting o the mixin circuit MCT.

Finally, the stop pulse is sent from the distributor TD over the stop segment of said distributor to the loop SL. This is a closed circuit pulse and operates through the relays TR and R to cause the armature of the latter relay to rest upon its marking contact and connect negative battery to the conductor ST. As will be described later in connection with the vacuum tube distributor VTD, this circuit will continue through the distributor to the conductor stp, and thence through the upper winding of the relay S and the lower or holding winding of the relay R to positive battery. Thus the complete code combination of seven pulses is sent to the line L.

In the meantime after the ith characterdetermining pulse is sent by the distributor TD,

the contact CC opens and after a sho-rt delay the relay CT releases, thereby unlocking the lower winding of the relay LR in the line circuit until the code combination for a new character is sent. During the brief period that the holding Winding of the relay LR is thus unlocked, it is possible for an operator at a distant station to send a break signal which will release the relay LR, and in a well-known manner obtain control of the circuit for transmission from the line L to the loop SL.

(f) Operation of the 'repeater when sending from the Zine L to the Zoop SII-start pulse In transmitting signals in the reverse direction, that is, from the line L to the loop SL, the operation is somewhat similar to that above set forth. However, the apparatus involved in the vacuum tube distributor VTD and that involved in` the mixing circuit MCT are in eiect reversed. Hence the signals from the line L now pass through the distributor and mixing 'circuit to the loop SL, instead of signals from the loop SL passing through the distributor and mixing circuit to the line L as previously described.

The operation of the distributor under these conditions is as follows:

When the transmitter MTS is stopped by opening the key CK so that it comes to rest, the line relay LR is unaffected by the Contact CC` and is therefore free to follow the incoming line signals. 'I'he distributor TD, of course, comes to rest on its stop Contact and in this position the contact CC is opened and remains open. Therefore, relay CC releases its contact and unlocks the relay LR by reducing the current iiow through its lower winding, so that a mere biasing effect is produced which can be overcome by current pulses from the line through the upper or operating winding of relay LR.

The function of the mixing circuit in this instance is to unscramble the scrambled impulses that come in from the line L after having been scrambled at a distant station. The cipher code combinations which are set up in the mixing circuit MCT for scrambling are the same as those used at the sending station, and when combined with the elect of the scrambled pulsesincoming 13 from the line, will cause the printer TTY to record the message in its normal or non-ciphered form.

The first impulse received from the line L will, of course, be a start pulse, i. e., an open circuit pulse. The normal current flowing through the upper winding of the relay LR will therefore cease, and the lower or biasing winding shifts the winding of said relay to its spacing contact. This completes a circuit from positive battery through a GOO-ohm resistance, through the lower winding of the relay RV, over the spacing contact of the relay LR, over the marking contact of relay TR, through the upper or operating winding of relay R, and through ano-ther 6fm-ohm resistance to negative battery.

At the time the circuit above traced is cornpleted, no current is flowing through the middle winding of the relay RV, and the upper winding is locked up through the 11,000-ohm resistance. This is sufficient to hold the armature of the relay RV on its lower or sending contactas long as there is no greater pull exerted in the opposite direction by one of the other windings. When signals were being sent from the loop SL to the line L as previously described, no current passed through the middle winding of the relay RV during the transmission of marking pulses, and during spacing impulses it was in such direction as to assist the upper Winding of relay RV to hold its armature upon its lower contact. l

However, under the condition of reception from the line L we now have, no current whatever flows through the middle winding of relay RV. Therefore, when current ilows thrcughvthe lower winding over the circuit above traced, the pull exerted by the lower winding is opposite in direction to that exerted by the upper winding, and is suiciently greater so that it overcomes the holding effect of said upper winding. The result is that the armature of relay RV is now shifted to its upper or sending contact in response to the first spacing signal received.

During reception from the line L, only spacingv impulses through the lower winding will operate upon the relay RV and no current will flow in the upper and middle windings. Therefore, the spacing pulses in the lower winding hold said armature in its upper position so long as signals are being received from the line L. In the marking condition the light biasing spring holds the armature of relay RV on its receiving contact. Therefore relay RV locks up the relay LS through its lower winding, thus preventing said relay from responding to signals from the relay S, but the lower winding of the relay TS receives no current. Therefore relay TS is able to follow the signals received by the relay S and transmit them into the loop SL.

The start signal current flowing through the upper Winding of the relay S causes its armature to be shifted to its spacing contact, thereby connecting positive current to the operating windings of relays TS and LS. Relay LS is disabled, but relay TS follows the signal and shifts its armature to its spacing contact, thus connecting positive battery to the junction point of the upper and lower windings of the relay TR. From this point a biasing current passes through the lower winding of said relay, through the 950-ohm resistance, and a 1,000-ohm resistanceto negative battery. No current flows through the upper winding of said relay TR because positive battery' is connected to the loop SL over the stop segment of the distributor TD. Hence the connection of transmitted by the relay TS. As will be shown later, said relay TR does not respond to a marking signal transmitted by the relay S, because the windings of the relay TR are balanced and oppose each other. dition of transmission from the line L to the loop SL, the relay TR is not actuated. The start signal produces Ya no-current condition in the loop SL as already described. This condition is Vequivalent to a start pulse in the subscribers loopfand the receiver TTY starts its cycle to receive the character-determining pulses which follow,

(g) Operation of the repeater when sending from Zine L to Zoop .SL-character determining pulses and stop impulses The iirst character-determining pulse now comes' in over the line L. Let us assume this is a'marking. pulse so that current flows through the upper or operating winding of the relay LR. This current is suiiicient to overcome the effect of the holding'current in the lower winding so that'the armature of the relay LR is now shifted to its marking contact. This completes a circuit' fromneg-ative battery over said contact, over the marking contact of the relay TR, and through the upper or operating winding of relay R to positive battery. Relay R shifts its armature toits marking contact and connects Nnegative battery over said contact to the conductor ST. AThe cir' cuit from this conductor extends throughv the vacuum tube 'distributor VTD in a manner to be later described, and thence over certain contacts and wiper brushes of the mixing circuit MCT- (depending upon its setting), thence over conductor 3 or B as the case may be to the upper winding ofrelay S, through a '775-ohm resistance, and through the lower windngof the relay R to positive batteryu The current through the lower winding of relay R is in such direction as to tend to hold the armature of said relay upon thecontact which established the circuit. In this case it tends to hold the armature upon the marking contact. The current through the operating winding of the relay S, however, without changing the direction of current through the lower Winding of the relay'LR, may be in either of two directions, depending upon the setting of the mixing circuit. Therefore it operates the armature of said In any event, due to the fact that the switches of the mixing circuit MCT are set in the same'way as the corresponding switches inthe mixing cir cuit at the distant sending station, the mixing circuit will determine that the direction of the current flow through the upper windings. of the relay LS will be in such direction as to restore the pulse received to non-ciphered condition. Thus if the original pulse, before scrambling, was a markingpulsethe currentfiowing through the upper windings of the' relay S will be in such direction as'to shift its armature to markingposition. This Vcauses the relay TS'to operate to marking position and connect battery to the midpoint of the windings of the relay TR.

Consequently,4 during the con-` From the midpoint of the windings of relay TR the circuit extends through the lower winding through a S50-ohm resistance, and through a LOGO-ohm resistance to fpositive battery. Similarly the current through the upper winding eX- tends through the l65-ohm and 400-ohm resistances, through the winding of the magnet of receiving teletypewriter TTY, and nally over the distributor brush and stop segment of distributor TD to positive battery. The current through the two windings of the relay TR produces equal and opposite effects so that the armature of said relay is not shifted. Current, however, flows through the subscribers loop SL through the upper winding of the relay TR as just described, thereby causing the receiving teletypewriter TTY to receive the first character-determining impulse as a marking signal.

In a similar manner the succeeding four character-determining impulses received from the line L are transmitted through the repeater, through the vacuum tube distributor VTD and mixing circuit MCT, as later described. These pulses operate the relay S to marking or Spacing as the case may be, thereby producing a corresponding marking or spacing signal in the loop SL. As these plulses have been restored to their original nonciphered form, the teletypewriter TTY prints the character originally originated at the sending station. A receiving station not equipped with the deciphering mixing circuit will, however, print some other character than that originally initiated, because the pulses will be received in scrambled form.

Following the last character-determining impulse the stop pulse is sent. This is a closed circuit or marking pulse and operates the relay LR to in turn cause the relay R to shift its armature to marking position. Negative battery is thus connected over the armature of the relay R to the conductor ST and through the distributor, in a manner to be described later, to the stop conductor stp. This conductor is connected to the conductor 3 leading to the terminal 3 of the upper winding of the relay S, and thence through said winding over a circuit previously traced to positive battery. Relay S, therefore, actuates its armature to its marking contact, in turn causing relay TS to send a marking signal into the loop SL, thus producing a stop signal for the receiving teletypewriter TTY. Y

(h) Operation of vacuum tube distributor VTD-start pulse When a code combination is transmitted either from the loop SL to the line L or vice versa, the relay R of the repeater responds as previously described to send, first, a start impulse which is a spacing signal. Consequently, a, circuit is completed from positive battery, over the space contact of the relay R, over conductor ST, over contact 6 of the start relay STT of the distributor, and thence over conductor ST', through the winding of relay R4, over contact 6 of relay R3, and over contact 2 of release relay REL to negative battery.

The current normally flowing through the winding of the relay R4 through the resistance a is insufficient to operate said relay. When, however, current ows through the winding of said relay over the circuit just traced, the total current flowing through the winding of the relay R4 is increased sufficiently to cause said relay to pull up its armature. When the relay R4 Ipulls upr its armature it will remain actuated by the current flowing through the resistance a even after the operating circuit above traced is opened at contact of relay STT as will be described later. It will remain so operated until the relay R3 later opens its contact 6 and thus open-circuits the relay R4, as will presently appear,

Relay R4 completes a circuit from positive battery, over its contact 2, over the contact 2 of start relay STT, through the winding of said relay, and thence over contact 2 of release relay REL to battery. Relay STT is at once energized and locked up over its contact I, so that it remains actuated during the complete cycle of the distributor, which involves all seven pulses of a code combination. It is not released until at the end of the cycle the release relay REL opens its circuit, as will be described later.

Normally, negative battery is connected over contact I of relay R4 to the starter anode of the orienting vacuum tube OVTz, thus short-circuiting the condenser C2. The relay R4 upon being energized, however, opens this short-circuit at its contact I, so that the condenser C2 is no longer short-circuited, Therefore, potential begins to build up from positive battery through the resistance T2 to charge condenser C2 high enough to ionize the path through the tube. This causes current to flow from negative battery to the main anode and through the tube OVTz to the plate oi said tube, thence over contact 3 of relay R3 and through the winding of said relay to positive battery.

The time required for the potential to build up upon the condenser vC2 will be from 2 to 16 milliseconds, depending upon the adjustment of the resistance T2. Therefore, when this period has elapsed the relay Rs will be energized as above described. At its contact I relay R3 will again connect negative potential to the start anode of the tube OVTz. This causes current flow through the tube to cease and disestablishes the original energizing circuit of relay Ra. Relay R3, however, upon energizing, opens its initial circuit at contact 3, and at contact 2 completes a locking cir'- cuit over back contact 2 of relay R1 to negative battery. Relay Rs will therefore remain locked up until relay R1 is operated, as will be later described.

At its contact B relay R3 opens the energizing circuit of relay R4, which at once releases. Finally, at its contact 4, relay R3 completes a circuit from negative battery, through condenser RC3 (which has been previously discharged over the contact 5 of relay R3), through the winding of the orienting relay OR, to positive battery. The condenser RC3 now gradually charges up, and during the time that it is being charged (an interval of approximately 4.4 milliseconds), the relay OR receives current and is operated.

Returning now to the start relay STT which was operated and locked up when the start impulse was initially received, said relay by opening its contact 4 and closing its contact 3, removes the negative potential which is normally applied through the resistance 1' to the start electrode of the timing vacuum tube TVT1. At its contact 3 relay STT closes a circuit from negative battery, over said contact 3, over conductor I0, contact of stop relay STP,`over conductor II, over the normal contact key K1', over the back left-hand contact of key K1, and thence to positive battery through the winding of the stepping magnet SM1 of the switch SW1 in the mixing circuit MCT. This prepares the switch 17 SW1 to be advanced one step at the end of the operation of the distributor, as will be later described.

The removal of the negative battery from the start anode of the tube TVT1 permits a potential to be gradually built up on the condenser C1 from positive battery through the resistances T1 and T1', which are adjusted so that this potential will reach a value to cause ionization of the tube TVT1 after a period of 22 milliseconds, this period corresponding to the time allowed for the start impulse. While this tube is thus being gradually built up to trigger olf, a start impulse will be relayed through the distributor over contact of the start relay STT when the orient ing relay OR operates as previously described. This occurs from 2 to 16 milliseconds after the above 22-millisecond start interval commences, depending upon the adjustment of the resistance T2 in the circuit of the orienting vacuum tube OV'Iz as previously pointed out.

Let us assume that this adjustment is such that said tube operates the orienting relay OR 8 milliseconds after the start pulse is initially re ceived from the relay R of the repeater. After this period has elapsed the start impulse is relayed through the distributor from positive battery, over the spacing contact of the relay R of the repeater, start conductor ST, over contact 5 of start relay STT, over contact B of the stop relay STP, over closed contact I of the orienting relay OR (which, as already stated, remains closed for about 4.4 milliseconds), over back con tact 4 of relay S1, over the heavy dotted line sti' to conductor 6, thence through the upper winding of relay S from terminal 6 to terminal 3, and thence through a '775-ohm resistance to negative battery through the lower winding of relay R.

This pulse lasts for 4.4 milliseconds while the condenser RC3 is charging up, and maintains the relay OR operated for this period of time. As soon as the condenser is fully charged, however, current ceases to ilow, and contact l of relay OR is opened so that the start pulse ends. The start pulse, however, is transmitted to relay LS or TS, as the case may be, to the line L or the loop SL, depending upon whether the signal was originated in the loop SL or came in from the line L.

Returning now to the vacuum tube TVT1, after 22 milliseconds have elapsed the condenser C1 has been charged up so that an arc is established for the control electrode (the electrode at the left) to the cathode (the lower right-hand electrode). The gas in the tube is now ionized and the resistance of the tube is broken down. This discharges the condenser C1 to put the tube TVT1 in condition to start its tuning cycle anew. At the same time a circuit is thus completed from negative battery to the cathode of the tube TVT1, through said tube to the plate thereof, and through the winding of relay R1 to positive ba*- tery. Relay R1 upon being energized opens at its Contact 2 the locking circuit previously traced for the relay R3, which is released. Relay R3 at its contact 4 opens the circuit of the relay OR i which is already released owing to the condenser RC3 being fully charged) and at contact 5 re, lay R3 completes the discharge circuit for the condenser RC3.

(i) Operation of vacuum tube distributor VTD character determining pulses Returning now to relay R1, said relay by closing its contact I initiates a new cycle of opera tions relating to the transmission ofthe rst of the five character-determining pulsesl Over its contact I relay R1completes a circuit from nega-y tive' battery, through the winding ofthe relay R2 to positive battery. Relay R2 upon being `en` ergized causes current to momentarilyi-low from' positive battery through the condenser RC2 (during the brief interval required for said condenser to be fully charged) over contact I of relay S1, through the winding of said relay, and over the contact 2 of release relay RELz to negative bat tery. The momentary impulse thus owing through the winding ofthe relay S1 increases the current through said winding suiciently to cause said relay to attract itsarmature. tures will be held up by said relay after the n10-- mentaryoperating pulse ceases, due to the .holdi ing current through the resistance r1. relay S1 will be in eiectlocked up until the-release relay REL operates at the end of the cycle of theV distributor, as will be described later. The relay" S1 changes the pulse distributing connections; of

the distributor as will presently appear.M

Returning to relay R2, immediately uponoperating said relay, at its contact I comprises afneg R4, over back contact 6 of relay, R3, and over contact 2l of release relay REL to lnegative,bat-j tery. Relay R4 (which/'had previously Ybeenreleased when relay R3 wasjactuated) isnowagain operated over the circuit just described,V VIt will' be held operated by the current through'therre, sistance a until the relay R3v is again operated, as will appear presently. At its contact I relay R1 again removes the negative Ashort--circuit from" the start electrodeof the orienting tube QVTz' to start the cycle of said tube anew.

In the meantime relay R2, havingY at its contact.l I short-circuited the windingof the relay R1 andA the plate circuit of the timingl tube TVT1, isre V leasedat contact Ifof relay R1 as soon as the.

relay R1 releases due to this short-circuiting ac'- tion. Relay Rz upon being released,nat`contact 3 opens the operating,circuitforrelay S1,jand at contact 2 opens the operating circuit for the reef lay R4. Relays S1 and R4 remain operated, however, due to the holding current through theirv At contact I,V relay R2 removes the short-circuit from the windvacuum,

respective resistances r1 and a.

ing of the relay R1 and the plate of the tube TVT1.

When, as previously described, the condenser C1 is discharged by the arc between the controlY electrode and the cathode, the 22-milliseco'ndV cycle of the tube TVT1 starts again as the-.condenser C1 begins to chargeup through the resistances T1 and T1'. The result is that, as before, the resistance of the tube breaks down at the end of another period of 22 milliseconds, andcurrent ows to the plate to again operate the relay R1 at the end of the 22-millisecond interval corresponding to the rst character-determining mplllSB.

In the meantime, before the vacuum tube TVT1 thus operates to terminate the 22-millisecond interval, condenser C2 associated with the orienting' tube OVTz is building up its charge, so that at the end of its adjusted periodV (which we have assumed to be 8 milliseconds) theresistance of said tube breaks down, and the operating circuit` Y .'of the relay R3 is again completed over the plate Said armarof the orienting tube OVTz. Relay R3 again locks up, short-circuits the tube OVTz over its contact I as before to discharge condenser C2, releases relay R4, and at contact 4 of relay R3 the 4.4- millisecond operating circuit of the relay OR is once more completed,

During this brief operation of the relay OR the rst character-determining impulse is transmitted. This impulse passes over the armature of the relay R, over conductor ST, over contact 5 of start relay STT, over contact 8 of stop relay STP, over contact I of relay OR, over contact 3 of now operated relay S1, over back contact 4 of relay S2, and thence to the conductor numbered I leading to switch SW4 of the mixing circuit. This circuit will be completed through the mixing circuit in a manner later to be described, and extended either over conductor 3 or conductor 6 associated with the relay S, to operate said relay. Relay S thus repeats the pulse (not enciphered) through the repeater to the line L or the loop SL, as the case may be.

At the end of 22 milliseconds the vacuum tube TVT1 again operates the relay R1 to initiate a new cycle of operations of the distributor corresponding to the second character-determining impulse. The relay R1 upon being operated, at its contact 2 opens the locking circuit for the relay R3, which is again restored to normal. By closing its contact I relay R1 again operates relay R2. Relay R2 at its contact I again short-circuits the winding of relay R1 and the plate circuit of the timing vacuum tube TVT1.

At its contact 3, relay R2 connects a momentary circuit from positive battery through the condenser RC2, over the front contact 2 of relay S1, over the back contact I of relay Sz, through the winding of said relay S2, and over the back contact 2 of release relay REL to negative battery. Relay Sz being thus operated, is held operated by the current through the resistance r2, and prepares a new path through the distributor over its contact 3, as will be described later. At its contact 2, relay Rz operates the relay R4, which, at its contact I, again disconnects negative batterey from the start electrode of tube OVTz. Said tube now commences its cycle anew to operate the orenting relay OR after 8 milliseconds of the next 22-millisecond interval has elapsed.

Meanwhile the winding of the relay R1, upon being short-circuited by the action of the relay Rz, releases the relay R2 immediately after it has been initially operated, and restores it to normal. The condenser C1 discharges in a manner previously described, so that the tube TVTi commences its 22-millisec0nd cycle for a third time, during which the second character-determining pulse is transmitted.

Thereafter, upon the operation of the orienting relay OR, the pulse circuit through the distributor is established for 4.4 milliseconds from positive or negative battery, as the case may be, over the armature of the relay R of the repeater, over conductor ST, contact 5 of relay STT, contact 8 of relay STP, contact I of relay ORfcontact 3 of relay S1, contact 3 of relay S2, contact 4 of relay S3 to t'ne conductor numbered 2 leading to switch SW4 of the mixing circuit. After passing through the mixing circuit in a manner appearing more fully hereafter, this circuit is completed through the upper winding of the relay S to operate it to marking or spacing in accordance with the character of the impulse received from the relay R as modified by the setting of the mix-- ing circuit MCT.

Without going into further detail, the vacuum tubes TVT1 and OVTz go through' their cycles and are then restored to normal to start cycles anew, until six 22-millisecond cycles are completed. The sixth cycle corresponds to the fth character-determining pulse of the received code combination. As these cycles are being executed the counting relays Ss, S4 and S5 are in turn operated. Therefore, during the period corresponding to the third character-determining cycle, the pulse from the armature of relay R passes over the circuit previously traced to the closed contact I of the orienting relay OR, and thence over contact il of relay S1, contact 3 of relay Sz, front contact of relay S3, and over the back contact 4 of relay S4 to conductor numbered 3 leading to the switch SW4. Likewise during the period corresponding to the fourth character-determining impulse, a similar circuit is completed over contact I of the relay OR, contact 3 of relay S1, contact 3 of relay S2, contact 3 of relay S3, contact 3 of relay S4, contact il of relay Ss, and over conductor numbered 4 t0 the switch SW4. Finally, during the period corresponding to the fth pulse, a similar circuit is established over contact I of relay OR, and over the No. 3 contacts of relays S1, S2, Ss, S4, and S5, and thence over the back contact of stop relay STP to conductor numbered 5 leading to the switch SW4.

(i) Operation of vacuum tube distributm VTD stop impulse Six 22-millsecond cycles have now been executed by the distributor apparatus, the time of each of these cycles being determined by the timing vacuum tube TVT1. The orienting vacuum tube OVTz at the proper time during each of these successive intervals distributes the start impulse and the iive character-determining impulses, respectively, over various contacts of the stepping relays of the distributor, as above described.

'When the last 22-millisecond interval has been completed, the vacuum tube TVT1 triggers olf and operates the relay R1, which, as before, releases relay R3 and operates relay R2. Relay Rz in turn operates relay R4 which starts the cycle of the orienting Vacuum tube OVTz. Finally, the relay R2, at its Contact I, short-circuits the winding-of the relay R1 and the plate circuit of the tube TVT1, releasing the relay R1. The relay R1 restores relay R2, so that the short-circuit at contact I of relay R2 is removed from said relay R1 and the vacuum tube TVT1. The vacuum tube has in the meantime started its cycle for the seventh time. As this cycle corresponds to the stop pulse, it must be made somewhat longer than the six preceding cycles.

This is accomplished in the following manner: While the relay R2 was energized in the manner just described, and before it was released, it completed a momentary circuit over its contact 3 from positive battery, through the condenser RC2, over the contact 3 of said relay Rz, over contact 2 of relay S1, contact 2 of relay S2, contact 2 of relay S3, contact 2 of relay S4, contact 2 of relay S5, thence over contact I of stop relay STP, and through the winding of said relay to negative battery over contact 2 of the release relay REL. The stop relay STP is now operated and holds up through its resistance b, but its initial energizing circuit is immediately thereafter reopened at contact 3 of relay R2 by the release of said relay R2, as above described.

Relay STP upon being energized, at its contact 6 opens the circuit previously traced for the stepping magnet SM1 of the switch SW1. The stepping magnet is now released and upon being released advances the brush B1 of said switch one step t change the setting of the mixing circuit MCT. At contact of stop relay STP, a circuit is established from negative battery, over contact 3 of start relay STT, over conductor I0, contact 5 of relay STP, over conductor I2 to the adjustable resistance T1. Resistance T1" is thus connected to negative battery in shunt with the condenser C1, which is also connected to negative battery. This retards the charging of the condenser C1 through the resistances T1 and T1. The result is that 31 milliseconds is now required to charge up said condenser to such potential that the tube TVT1 will trigger 01T and operate the relay R1.

In the meantime, by the closing of its contact l, stop relay STP prepares a circuit which, upon the operation of the orienting relay OR, sends a stop impulse to the relay S of the repeater as follows: From negative battery, over contact 3 of relay STT, over conductor I0, over contact 'l of relay STP, over contact I of orienting relay OR, over contacts numbered 3 of relays S1, S2, Ss, S1, S5 and STP, thence over the stop conductor stip and over conductor 3, through the winding of relay S from terminal 3 to terminal 6, and thence to positive battery through the lower winding of the relay R to positive battery. By the operation of the relay S over the circuit above traced, a stop impulse is sent to the line L or the loop SL, as the case may be.

At the end of the 31millisecond interval the timing vacuum tube TVT1 operates the relay R1, which in turn operates the relay R2. Relay R2 shorts the relay R1 and the vacuum tube TVT1 as before, at its contact I. At contact 2 relay R2 operates the relay R4, and at contact 3 it completes a momentary operating circuit from positive battery through condenser RC2, over said contact 3 of relay R2, over No. 2 contacts of relays S1, S2, S3, S4, S5 and STP, and thence over the contact I of release relay REL and through the winding of said relay to negative battery over contact 2 of said relay REL.

The relay REL at once opens its contacts I and 2, thereby restoring the following relays to normal-relays STT, S1, S3, S5, REL, R4, S2, S4 and STP, each of these relays having its circuit connected to negative battery over the contact 2 of relay REL. In the meantime relay R2, having short-circuted relay R1, the latter upon releasing immediately opens the circuit of relay R2 and restores it to normal. Relay Rs was, of course, released by the opening of contact 2 of relay R1 during its momentary operation. Thus` all elements of the distributor VTD are restored to normal, and are ready to receive a new combination of seven pulses.

(lc) Operation of the mixing circuit MCT- stepping of switches It will be recalled that at the beginning of the operation of the vacuum tube distributor V'ID, the operation of the relay STT, upon the initiation of the cycle .of the operations of the distributor, closed a circuit over contact 3 of relay STT, over conductor III, contact 6 of stop relay STP, over conductor II, and through the winding of the stepping magnet SM1 of the switch SW1 of the mixing circuit MCT. The energization of Ythis magnet does not advance the brush".

B1 of the switch at this time, but said brush is advanced one step when the stepping magnet'SM1 is released upon the operation of the stop relay STP, after the ve character-determining pulses have been distributed. Thus the brush B1 Vof the switch SW1 is advanced one step for each character received by the distributor.

The switch SW1 has 22 steps, and after the brush has reached its twenty-second position the brush is advanced and cornes to rest again upon the first set of contacts. While the brush was resting on the contacts of the twenty-'second po'- sitonof the switch SW1, a circuit wascompleted over it's zero wiper, from negative battery, over said wiper, over contact 22, conductor I3, normal right-hand contact of key K1, normal left-hand contact of key K2, and through the winding of stepping magnet SM2 to positive battery. The stepping magnet of the second switch SW2 is thus energized, and when the brush of theswitch SW1 when the brush B2 passes from its twenty-second` A position to its iirst position.V In this manner the brush Ba of the switch SW3 is advanced one step each time the brush of the switch SW2 completes a cycle.

In like manner, each time the brush of the switch SW3 completes a cycle, it closes and then opens the circuit of the 'stepping magnet SM4 of the switch SW4 to advance theVV brush B4 of the' switch SW4 one step. In this manner` the brush of the switch SW1 is advanced step-by-step until all of the code combinations have been used.`

When the brush of the switch SW1` has been stepped through al1 of its twenty-two positions,

, the next 'step restores it to the No. l position,

and rthe entire cycle of operations of lthe four switches may be repeated.

By actuating and then releasing the key K1', the magnet SM1 will advance the brush B1 of the switch SW1 one step. In this manner the brush may be advanced step-by-step to any position desired. By using the similar keys associated v with the other switches, any one of them lmay be advanced step-by-step to any chosen position.

Also, by operating a key such as K1, the magnet SM1 will advance the brush of the switch SVI/1' step-by-step automatically. When the key K1 is operated a self-interrupting circuit is controlled by the armature of said magnet SM1 until the brush is advanced through a complete cycle of its No.k 22 position. In this position magnet SM1v is locked up over the zero wiper of brush B1, con-l tact 22 and conductor I3 until the key K1 is released, whereupon the switch advances to its No. I position and there remains. The circuits by which these operations are performed are obvious, and as they form no part of the present invention, need not be further described. (l) Operation of mixing circuit MCT- scrambling action of switches SW4 and SW3 It will pe recaued thatthe ave successive character-determining pulses of the code combination were applied in regular order by the vacuum tube distributor VTD to the heavy line conductors, l 2, 3', 4 and 5 which lead to the ve correspondingly numbered contacts in the upper row of the switch SW4. The numbers applied to the corresponding five contacts in the other rows are arranged in diierent order for each row, and all of the contacts bearing the same number are wired together. For example, in the diagram for switch SW4 the wiring for the No. l segment only is shown carried throughout the various rows of contacts of the switch. However, it will be understood that the contacts numbered 2, 3, 4 and will be similarly wired through the switch, all No. 2 contacts being wired together, all No. 3 contacts being so Wired, and so forth.

The result is that as the pulses pass from the heavy conductors numbered i, 2, 3, 4 and 5, respectively, to a given set of contacts, and over the correspondingly numbered wipers of the brush B4, the original five pulses are scrambled to transmit on to the next switch a different code combination than the one originally applied to the switch SW4. The code combination to which the original combination is thus translated depends upon the setting of the brush B4 and upon the order in which the contacts for that settingr are arranged.

The switch SW3 acts to further scramble the set of pulses. For example, the pulses picked up by the five wipers of the brush B4 are transmitted over the wires numbered I, 2, 3, 4 and 5 leading to the wipers of the brush B3 of the switch SW3.

Here again it will be seen that the numbers ap plied to the five contacts corresponding to the character code combinations are differently wired in each row. Only the wiring for contacts 4 and 5 are actually shown, but it will be understood that the contacts numbered I, 2 and 3 will also be wired through the switch. In each instance all contacts having the same number will be wired together. The result of this is that depending upon the setting of the brush Ba of the switch SW3, the original ve pulses which have been scrambled once will be scrambled again in a different manner. The pulses thus twice scrambled are applied to the conductors l, 2, 3, 4 and 5 leading to the correspondingly numbered wipers of the brush B1 of switch SW1.

(m) Operation of mz'ing circuit--pulse reversing operation, of switches SW1 and SW2 It is the function of the switch SW1 to determine in effect whether the pulses thus transmtted to the Wipers of the brush B1 shall individually be marking or spacing impulses. To this end four of the ve character-determining contacts in each row of the switch SW1 are numbered either 3 or 6, the numbers varying from row to row. All contacts numbered 3 are wired together and connected to the conductor 3 leading to terminal 3 of the relay S. Likewise all contacts numbered 6 are wired together and are connected to the conductor 5 leading to the terminal No. 6 of the relay S, This means that any of the scrambled impulses coming in over one of the conductors such as No. l to the wiper No. I of brush B1, may be in effect reversed or not reversed in polarity, depending upon the number of the contact upon which the wiper of the brush B1 rests. Thus a further encipherment is effected.

In order to introduce further complexity into the mode of encipherment, one of the five char- 24 acter-determining contacts of each row of the switch SW1 is marked XL All of the contacts marked X in the same vertical row are wired together and in turn are wired to one of the conductors numbered l, 2, 3, 4, and 5, leading to the wipers of the brush B2 of switch SW2. For example, all of the X contacts in the rst vertical level to the right are connected to conductor 5. All of the X contacts in the second row to the right are connected to conductor 4, and so forth.

The five character-determining contacts of each row of switch SW2 are marked either 6 or 3. Again all of the contacts marked 8 are wired together and to the conductor 6 leading to terminal 6 of the relay S. Likewise all ofthe contacts marked 3 are wired together and connected to the conductor 3 leading to terminal 3 of the relay S. Thus one of the five impulses passing through the switch SW1 over a contact marked X will, by means of the switch SW2, be in eifect again reversed or not reversed in polarity, depending upon the setting of the brush Bz.

To summarize, it will be seen that each combination of ive character-determining pulses is subjected to a plurality of changes after leaving the distributor VTD and before arriving at the relay S. Each pulse is subjected to two scrambling operations, one by the switch SW4 and the other by the switch SW3. Then the pulsel is` subjeoted to a possible polarity reversal by the action of the switch SW1 before being' applied to the relay S. Moreover, in some instances (where the pulse passed through an X contact of-the switch SW1) the pulse is subjected to a further possible polarity reversal by means of the switch SW2, before arriving at the relay S. Hence various changes will depend upon the relative setting of the brushes of the several switches. Also they will be varied for each successive character to be transmitted because of the automatic stepby-step action of the switches already described.

(n) Operation, of mixing circuit MCT-paths for individual pulses In order to more readily understand the nature of these changes, let us trace one vof the character-determining pulses through the entire circuit. Assume that a code combination has been set up in the loop SL of which the first character-determining impulse is a marking impulse. Relay TR accordingly transmits a marking impulse to the relay R, which in turn causes its armature to rest on its marking contact so that negative battery is apliedto the armature. If no scrambling or reversing eifects were to be introduced, this pulse would be directly applied to the terminal 3 of the upper winding of relay S, causing the relay S to transmit to the line L a marking signal. If, however, the pulse had been a spacing pulse, the armature of relay R` would rest upon its spacing contact and positive battery would be connected to terminal 3 of the upper winding of the relay S to send a spacing signal.

Actually, however, the circuit as wired does not transmit the pulses from the armature of relay R directly to the `upper winding of the relay S, but they are subjected to a scrambling and reversing operation. Therefore, when the relay R moves this armature, as above described, to Iits marking Contact, negative battery is applied to the conductor ST. If the pulse in question is the iirst character-determining pulse, the distribu-v tor will have started through its cycle already described and the relays, STT and S1 will have been operated and locked up. When. due to the ao- 25 tion of the timing vacuum tube TVT1 and the orienting vacuum tube OVTa the relay OR closes its contact I, the negative current will pass from the armature of relay R over the conductor ST, over contact of the relay STT, contact 8 of the relay STP, contact I of the orienting relay OR, contact 3 of the relay S1, contact 4 of the relay S2, and over heavy conductor numbered I to contact I of the upper row of the switch SW4.

If we now assume that the brushes of the four switches are in the position shown in the diagram, the negative current will continue over the contacts of the switch SW4 which are numbered I, to the contact numbered I in the sixteenth rofw. At this point contact numbered I is out of sequence, being in the second position instead of the first. Consequently, the negative current ows from contact I in the sixteenth row, over wiper No. 2 of brush B4, over conductor No. 2 leading to the wiper No. 2 of the brush Ba to the contact marked 5 in the ninth row of switch SW3.

All of the contacts numbered 5 in this switch are wired together, and are connected to the conductor numbered 5 leading from the switch SW3 to the brush B1 of the switch SW1. Therefore, the negative current continues over said conductor No. 5 to wiper No. 5 of brush B1, which, in this particular instance, is resting upon the contact in the second row marked X. From this contact, which is in the fifth vertical row, negative current ilows over the conductor numbered 5 leading to wiper 5 of brush B2 of switch SW2. The brush Bz is in the fourteenth position, and in this position brush No. 5 is resting upon contact numbered Ii. The negative current, therefore, continues over the segments numbered 6 of switch SW2 to conductor 6 leading to terminal No. 6 of relay S, and thence through the upper winding of said relay, through a l775-ohm resistance, and through the lower winding of relay R to positive battery.

If we assume that without any ciphering effect the negative current would have been applied to terminal 3 of relay S to transmit a marking signal to the line L, it is obvious that the first pulse has been reversed because it has passed through the upper winding of the relay S in reverse direction. Therefore, the relay S will send a spacing signal to the line instead of a marking signal.

Now let us assume that the distributor has advanced in its cycle to transmit the second character-determining pulse. Under these conditions not only relays STT and S1 are locked up l but relay S2 has been operated and locked up.

Let us assume that the second pulse transmitted by the relay R is a spacing pulse. Then positive current will be transmitted over the armature of relay R, over conductor ST, over contact 5 of relay STT, over contact 5 of relay STP, over contact I of the orienting relay OR, over contact 3 of relay S1, over contact 3 of relay S2, and over contact 4 of relay S3 to heavy conductor No. 2 leading to the No. 2 contacts of the switch SW-i.

With the brush B4 in the position shown, the positive battery coming over heavy conductor 2 will be applied to the third character-determin. ing contact of the sixteenth row. From this point the current flows over wiper No. 3 of brush B4, over the conductor marked No. 3, and over wiper 3 of brush Bs to contact numbered I in the ninth horizontal row of the switch SW3. From this contact the positive current passes over the No, I

contacts of the switch SW3 over the conductor numbered I leading from the switch SW3 to the switch SW1, over wiper No. I of the brush B1 of the switch SW1 to the contact numbered 3 in the Vertical row of contacts of the switch SW1.

Thiscontact is the second from the left, thus being in effect the first character-determining` contact for that switch. From this contact numf The original signa-l initiated by the relay R wasV also a spacing signal. Thus it is seen that after the various scrambling and reversing operations, this particular pulse comes out without change. However, it will be recognized that in some other setting'of the switches it might have been applied to the conductor 6, in which case the current would flow through the upper winding of the relay S in reverse direction, thus sending a marking signal instead of a spacing signal.

Without following through the other three character-determining impulses of the code combination, it will be evident that each of the pulses is subjected to successive scrambling and revers-` ing operations which may result either in transmitting the pulse normally or in reversing it, depending upon the setting of the switches. For certain settings the Vscrambling and reversing operations will in effect merely cancel each other out with respect to some pulses. In the case of other pulses, with the same setting the scrambling and reversing eiects may not cancel each other out, in which case the pulses affected will be reversed.V f

However, what happens to any given pulse depends upon the setting of all the switches of the mixing circuit MCT. As there is an enormous number of possible settings of the switches, each successive code combination will be scrambled in some arbitrary but diierent manner, because the switches change their relative settings a step at a time each time a new code combination is transmitted. Moreover, if a code combination correspending to a particular character is sent by the relay R and is enciphered in a particular way, then if that character is at once repeated, the setting of the switches will be changed and it will be enciphered in a different manner.

Summarizing the eiect of the mixing circuit MCT as a whole, it may be thought of as substituting for the real character combination some other combination determined by they setting of the switches of the mixing circuit. This combi' nation, determined by the mixing circuit, is varied each time another character is transmitted, Moreover, the variations introduced by the mix-Vy ing circuit follow each other in `an arbitraryA order. Furthermore the complete sequence Yof successive enciphering character combinations set up by the mixing circuit will not be repeated in the same order until the several switches have been stepped through all of the enormous number of possible relative positions of which they are capable. It will be understood, of course, that the numbered connections applied to the contacts ofthe switches are suggestive only and that theymay 27 be arranged in many other diierent combinations.

While this invention has been disclosed in certain specific arrangements which are deemed desirable, it will be obvious that the general principles herein set forth may be embodied in many other organizations, widely different from those illustrated, without departing from the spirit of the invention as deiined in the appended claims.

What is claimed is:

l. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, means to encipher said code combinations by varying the character of component impulses in an arbitrary manner, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination.

2. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, means to encipher said code combinations by varying the character of component impulses in an arbitrary manner, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, and means operating to cause said vacuum tube to produce at least one timed interval in the code cycle differing in duration from the others.

3. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in munber but variable in character, means to encipher said code combinations by varying the character of component impulses in an arbitrary manner, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a, group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, all of said timed intervals but one being of equal duration.

4. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, means to encipher said code combinations by varying the character of component impulses in a random manner, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, and means operating at the end of each interval to '28 shift the connection of said common circuit to a different one of said individual circuits.

5. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, means to encipher said code combinations by varying the character of component impulses in an arbitrary manner, and a distributor for transferring the impulses of a code combination one at a'time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated 4timing circuits so related that said vacuum tube will produce a, succession of timed intervals one corresponding to each impulse of a code combination, means operating to cause said vacuum tube lto produce at least one timed interval in the code cycle differing in duration from the others, and means operating at the end of each interval to shift the connection of said common circuit to a different one of said individual circuits.

6. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, means to enipher said code combinations by varying the character of component impulses in an arbitrary manner, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum Itube and associated timing circuits so related that said vacuum tube Will produce a succession of timed intervals one corresponding to each impulse of a code combination, all of seid timed intervals but one being of equal duration, and means operating at the-end of each interval to shift the connection of said common circuit to a different one of `said individual circuits.

7. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse oi a code combination, and means operating to cause said vacuum tube to produce at least one timed interval in the code cycle diiering in duration from the others.

8. In a signaling system, Ya common circuit upon which a plurality of combinations or impulses are impressed, said code combinations comprising a cycle .of successive impulses uniA form in number but variable in character, and a. distributor for transferring the impulses ofa code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, means operating to cause said vacuum tube to produce at least one timed interval in the code cycle differing in duration from the others, and means operating at the end of each interval to shift the connection of said common circuit to a diierent one of said individual circuits.

9. In a signaling system, a common circuit upon which a plurality of combinations of irnpulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, means operating to cause said vacuum tube to produce at least one timed interval in the code cycle ditering in duration from the others, and a second vacuum tube and associated timing circuit so adjusted as to send a pulse of predetermined length during a particular period of each of said timed intervals.

10. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but Variable in character, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, said distributor including a vacuum tube and associated timing circuits so related that said vacuum tube will produce a succession of timed intervals one corresponding to each impulse of a code combination, and means operating to cause said vacuum tube to produce at least one timed interval in the code cycle differing in duration from the others, a second vacuum tube and associated timing circuit so adjusted as to send a pulse of predetermined length during a particular period of each of said timed intervals, and means to shift said period to various portions of said intervals.

11. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, a multipoint switch having connections at each point to extend said individual circuits separately to a second group of individual circuits, the connections between circuits in said'groups varying from point to point of said switch, a relay for transmitting marking and spacing pulses to another common circuit, an additional multipoint switch having connections at each point to connect certain circuits of said second group to said relay so as to cause it to send marking pulses for a given set of connections between the circuits of the two groups, and having other connections at each point to connect other circuits of said second group to said relay so as to cause it to send spacing pulses for said given set of connections between circuits of the two groups, said connections of said additional multipoint switch varying from point to point.

12. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a distributor fo-r transferring the impulses of a mon circuit to individual circuits of a group of circuits, av plurality of multipoint switches each having connections at each point throughwhich said individual circuits may be separately extended to4 a second group ofA individual circuits, the connections between circuits injsaid groups varying from point to point in each of said switches, a relay for transmitting marking and spacing pulses to` another common circuit, an additional multipoint switch having connections at each point to connect certain circuits of said secondgroup to said relay so as to cause it to send marking pulses for a given set of connections vbetween the circuits of the two groups and having other connections at each point to connect other circuits of said second group to said relay so as to cause it to send spacing pulses for said given set of connections between circuits of the two groups, said connections of said additional multipoint switch varying from point to point.

13. In a signaling system, a common circuit upon which aplurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a -distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, a multipoint switch having connections at each point to extend said individual circuits .multipoint switch having connections at each point to connect certain circuits of said second group to said relay so as to cause it to send marking pulses for a given set of connections between the circuits of the two groups, and having other connections at each point to connect other circuits of said second groupto said relay so as to cause it to send spacing pulses for said given set of connections between circuits of the two groups, said additional switch also having at least one connection at each point extending to a second additional multipoint switch, said second additional switch having connections to said relay at each point to determine whether a given pulse sent therethrough will cause said relay to send a marking or spacing pulse, said connections of both said additional multipoint switches varying from point to point. y

14. In a signaling system, a common circuit upon which a plurality of combinations of impulses are impressed, said code combinations comprising a cycle of successive impulses uniform in number but variable in character, and a distributor for transferring the impulses of a code combination one at a time from said common circuit to individual circuits of a group of circuits, a plurality of multipoint'switches each having connections at each point through which said individual circuits may be separately extended to a second group of individual circuits, the connections between circuits in said groups varying from point to point in each of said switches, a relay for transmitting marking and spacing pulses to another common circuit, an additional multipoint switch having connections at each point to connect certain circuits of said second group to said relay so as to cause it to send marking pulses for a given set of connections between the circuits of the two groups, 'and each point to determine whether a given pulse sent therethrough will cause said relay to send a. marking or spacing pulse, said connections of both said additional multipoint switches varying 5 from point to point.

CLAUDE IRVING CRONBURG. 

